Conventionally, various touch panels which can simultaneously detect a touch position and a pressing force have been proposed. For example, WO 2013/021835 A discloses a touch panel configured such that a pressure sensor unit for detecting a pressing force is overlaid on a capacitive touch panel unit for detecting a touch position.
FIG. 16(A) is a side sectional view schematically illustrating the touch panel of WO 2013/021835. The touch panel 300 includes a plurality of films 301, 302, 303, 304, and 305. The films 301, 302, 303, 304, and 305 are laminated in order from a top surface to a bottom surface, and are bonded to each other with an adhesive sheet interposed therebetween.
The films 301 and 302 form a capacitive touch panel unit. A plurality of touch panel electrodes 311 are provided on the top surface of the film 301. A plurality of touch panel electrodes 312 are provided on the top surface of the film 302. The touch panel electrodes 311 and the touch panel electrodes 312 are arranged to cross each other in a two-dimensional lattice viewed from the top surface of the display panel. When a finger or the like approaches the touch panel 300 while a pulse signal is applied between each of the touch panel electrodes 312 and each of the touch panel electrodes 311, capacitance between the touch panel electrode 312 and the touch panel electrode 311 changes in the vicinity of the touch position. As a result, the touch position can be detected by detecting the change in the capacitance.
The films 303, 304, and 305 form a pressure sensor unit. Specifically, a pressure sensor electrode 313 is provided on the entire top surface of the film 303. A pressure sensor electrode 314 is provided on the entire top surface of the film 305. The film 304 is made of a material having piezoelectricity for generating charges on the top surface and the bottom surface as a function of the extension and contraction of the film 304 in the in-plane direction. When the touch panel 300 is pressed with a finger or the like, charges are generated on the top and bottom surfaces of the film 304 and a potential difference is created between the pressure sensor electrode 313 and the pressure sensor electrode 314. Accordingly, the pressing force can be detected by detecting the potential difference between the pressure sensor electrode 313 and the pressure sensor electrode 314.